Study: 100% renewables doesn’t equal zero-carbon energy

While 160 companies around the world have committed to use “100 percent renewable energy,” that does not mean “100 percent carbon-free energy.” The difference will grow as power grids become less reliant on fossil power, according to a new Stanford study published in Joule. Entities committed to fighting climate change can and should measure the environmental benefits of their renewable strategies accurately, the authors write.

Current methods of estimating greenhouse gas emissions use yearly averages, even though the carbon content of electricity on the grid can vary a lot over the course of a day in some locations. By 2025, the use of yearly averages in California could overstate the carbon reductions associated with solar power by more than 50 percent when compared to hourly averages, the paper shows. One finding of this analysis is that wind power – not solar – needs to be the next wave of investments for California. Similar analyses could suggest different options like nuclear power, geothermal energy, and long-range transmission in other locations.

“To guarantee 100 percent emissions reductions from renewable energy, power consumption needs to be matched with renewable generation on an hourly basis,” said Sally Benson, co-author of the paper and co-director of the Precourt Institute for Energy.

“Just purchasing more solar energy in a grid that already has lots of solar generation will not result in zero emissions,” Benson, professor in the Energy Resources Engineering Department in the School of Earth, Energy & Environmental Sciences, also said.

Annual vs. hourly accounting

Corporations that claim to be 100 percent renewable do not actually cover all their power use with renewables, as some acknowledge. Instead, they purchase or generate enough renewable energy to match 100 percent or more of their electricity use over the course of the year. For energy purchases dominated by solar power, an entity generates far more electricity than it uses during the afternoon and sells the excess. Then at nighttime it purchases power from the grid, which is much more carbon-intensive if generated by burning of fossil fuels.

The use of annual averages of the carbon content of grid power is valid only when fluctuations in renewable generation are small, or when all excess renewables can be stored. Places like California, Hawaii and some European countries experience large fluctuations in carbon content due to existing renewables, and do not yet have enough storage capacity to capture all excess electricity. In California, intentional reductions in solar and wind production, or “curtailments,” reached 3 percent of total generated energy in two months last year, the paper cites.

The difference in environmental benefit between wind and solar in today’s accounting methods therefore doesn’t account for the time of day when power is delivered. Instead, the difference between emissions reductions from wind and solar generation is only related to the difference in carbon footprint between the two technologies.

“Both the carbon footprint of a large consumer and the environmental value of renewable energy assets depend on the grid they interact with,” said energy resources engineering PhD student Jacques de Chalendar, lead author of the study. “Using hourly data is the best way to measure the environmental benefit of renewables, and this will become increasingly true wherever renewable generation is growing.”

Investing in non-solar renewables

The problem with investing in more solar panels in California is that the output often will not cause fossil fuel based generators to turn off, because they are already idle at the time of day the solar panels will produce power. In the paper’s case study, which approximated a hypothetical 1 megawatt constant load in California, short-term annual and hourly carbon estimates did not show significant differences in 2018. But by 2025, the two methods of estimation varied widely.

Using annual accounting, a 100 percent solar strategy in 2025 would reduce carbon emissions by 119 percent of the hypothetical company’s carbon footprint. Using hourly emissions, though, the number shrinks to 66 percent, according to the study. For a 100 percent wind power strategy, annual averages indicate 131 percent carbon reductions, which actually jumps to 135 percent using hourly data.

“In California, gas is often the marginal generation source and has a higher emissions rate than average grid power, which is why purchasing renewables can result in a net negative carbon footprint,” said de Chalendar. “A consumer with a 100 percent renewable energy supply can actually reduce the carbon footprint of the grid in addition to their own carbon footprint.”

Energy storage

Hourly carbon accounting methods could help large consumers increase their use of low-carbon power from the grid. With more accurate information, consumers can move flexible consumption to times of the day when grid power is cleanest. The data could also help consumers decide whether they should invest in large-scale energy storage projects as the most economical way to meet their carbon targets. This is because energy storage allows consumers to draw electricity from the grid during low-carbon periods and store it for later use.

Stanford University, for example, recently electrified its heating and cooling system and added thermal storage to cut emissions to a third of their 2014 peak levels. By using its energy storage to maximize purchases of electricity in the afternoon when solar power dominates the California grid, Stanford could reduce emissions from heating and cooling by an additional 40 percent, according to a study published earlier this month by the authors of this paper.

Location-specific analyses might suggest different types of low-carbon investments and strategies for other regions, the paper notes. In Great Britain, for example, grid carbon intensity is currently lower at night, meaning different types of renewable investments or consumption behaviors might be better. Alternatively, long-range transmission of electricity could also allow entities to transport low-carbon electricity elsewhere when there is an oversupply and receive low-carbon electricity when there is a minimal amount of renewable electricity generation.

“Transparent, precise and meaningful carbon accounting is necessary,” Benson said. “And if it’s done properly, we can make the right investments in renewable power and create a more sustainable grid.”

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All data and supplemental code used in their commentary are publicly available here.

What in hell is going on at the Stanford engineering schools? “Power consumption needs to be matched with renewable generation on an hourly basis?” Does that mean 10-to-12 hour blackout periods on a daily basis? And higher and higher energy prices? Because with the overall percentage of wind/solar’s share of the power generated everywhere, especially in this country, being so small, and considering the total unsuitability of wind/solar as a reliable, constant base power source, the strategy of these so-called mediocrities who are posing as engineers will result in exactly that – and get no one closer to 100% renewable power.

What in hell is going on at the Stanford engineering schools?
Larry, the same thing that is going on with all the schools.
Schools preach theory and hypotheticals. These aren’t actual grid engineers who actually make this stuff work.

Where do you think the steel other materials manufacturing, maintenance, transportation for the so called zero carbon options come from? The cradle to grave carbon footprint of most renewables is often greater than conventional power. Also, the claimed lifespan is often far shorter.

Exactly wind and solar will never repay their carbon debt across their life time. It quite wimple it take more energy to produce and install them that they will every produce, that is why the will never be installed or used without direct subsidies!

This is the case of electricity generated by wind power for sure. People tend to think, even in this study, that Aerogenerators appear in the hills by spontaneous generation. The so called “carbon footprint” or “environmental default” of these things is huge considering raw materials, even without take the first rotation. Check how Neodymium and Dysprosium or Therbium are obtained in Bayan Obo and refined in Baotou… Sorry “Stanford” but I risk to say that the greenhouse gas emissions should be accounted from the first gram of earth that need to be displaced to obtain raw materials to make Aerogenerators possible. Probably it would be surprises by checking how these things perform even compared with Black Coal.
These things are nowadays one of the biggest source of radioactive waste from Monazite and Bastnasite processing to obtain lanthanides.

Loydo, yes there is plenty of evidence
that proves that the carbon footprint of a wind turbine is greater than a fossil fuel equivalent. If you can’t see that yourself I really do despair. Just venture outside your goldfish bowl and do the maths. If you can’t be bothered to look I’m damned if I’m going to do it for you

They might be right but its up to them to back up their claims, otherwise its just arm-waving.
This: “carbon footprint of most renewables is often greater than conventional power” sounds completely made up to me. If Mark is basing it on some research he’s already done then I’m sure he won’t mind sharing it to save everyone else the trouble.

None required really, just common sense. Since wind and solar has to be backed up 24/7 by equivalent capacity fossil plants to avoid blackouts when the weather fails, they by definition cannot have a lower footprint than the very same fossil plants. See here in more detail:

“The problem with investing in more solar panels in California is that the output often will not cause fossil fuel based generators to turn off, because they are already idle at the time of day the solar panels will produce power.”

stop…..how did this many people get this stupid…..it’s not our problem

we have not contributed one molecule toward the increase in CO2 in over a decade

Global warming does not care how many people you have…only how much CO2 is put in the air
..and China, India, and the rest of the developing world are now putting 6 times as much CO2 in the air as the USA

per capita = reparations……if it’s reparations….then it has nothing to do with global warming

No one in their right mind would say your neighbors get to pollute more because they have a bigger family…..

the whole “per capita” argument is asinine…obvious…and a scam
…the people pushing it..can’t possibly believe the crap they are pushing about global warming being dangerous

“global warming does not care how many people you have
…only how much CO2 is put in the air”

Nope. Its how much ‘has’ been put in the air. You can’t just airbrush out the historic facts.

“No one in their right mind would say your neighbors get to pollute more because they have a bigger family…..”

Bs. By the same token they shouldn’t eat more food, draw more water or use more fuel?

“the whole “per capita” argument is asinine”

Only to a few selfish, energy profligate Americans, Canadians and Australians. To billions of others it makes perfect sense. What if China broke up into three countries, each with the same population as the US, each emitting way less CO2 than the USA? Still not our problem? Never is, but thats exceptionalism for you.

CO2 emissions per country is asinine.

Profits are best counted per capita but emissions should be socialised – counted per country. I though you were against socialism.

Not true, we still are contributing. just we have reduced out contribution, we are still contributing it not at zero, if everyone had done this CO2 would have done one of four thing, first stabilized, second reduced, third increased slower and fourth keep going the way it is. This is not refutable, the problem is no one can tell you which one of the four would have had happen. No one know how much of the CO2 increase is due to man. Not only that to the most part we don’t know why the past fluctuations have occurred since one celled animals started taking CO2 out of the atmosphere and free oxygen became available, we know there was a big drop at that point that when all the iron in the oceans oxidized and now we have large formations of red rock. We know what caused that drop, as to the other there are only a guesses.

There is no time of day when fossil fuel based generators are turned off. Fossil fuel plants can’t be turned off and on like that. What happens is that the CA utilities have to pay other states to take their excess electricity.

MarkW posts: “There is no time of day when fossil fuel based generators are turned off.”
…
MarkW has never heard of “peaking power plants,” almost all of which use fossil fuel.
…https://en.wikipedia.org/wiki/Peaking_power_plant
….
“Peaker plants are generally gas turbines that burn natural gas.”

Please, cut him a little slack; although unstated, his reference was most likely to base load fossil fuel plants, like coal and larger gas-fired steam-boiler based plants. To operate those plants most economically “thermal inertia” dictates that those type of plants operate continuously.

You you may be new here, IDK, but MarkW has been here for quite some time and has an establish ‘track record’. Maybe you are having a not so good day, your goldfish died or the stock market took a downturn in your market segment, in any case, have a better day.

Much Ado about nothing. Electrical grid emissions are tiny compared to transportation emissions and all CA emissions are only 1 percent of the world’s emissions. Like a pebble in the ocean.
Stanford should work on something more meaningful.

I’m so confused! This report sounds like it is made up of the clever use use of “mathe-magics” and advanced “Unicorn-linguistics” using a liberal application of the equals sign (=) when ever it “feels dramatically correct” (ie. PC) to do so. 119%!,….130%!??? What the Freud?

The report is simple. It says that when electricity generation is 100% renewable, there will be periods when no electricity is available. Users will therefore have to change their usage patterns accordingly.

The report did not go onto how those industries that must operate continuously can survive. That’s because they won’t be able to survive. So we will all have to learn to do without any metals. We won’t be able to use plastics instead, of course, because plastics come from fossil fuels.

Message to politicians: For goodness sake, wake up!!! You are sleep-walking us to oblivion.

Solar power is like a ketchup bottle
First you get a little, then you get a lottle

Unless you can transport the electricity to where the sun ain’t shinin’, there comes a point where adding more solar is usless without adding storage for its output. I imagine the economics of that is not pretty.

The greenies’ obsession with Carbon and CO2, and how they confuse the two with no understanding of their differences, no understanding of the millions of organic compounds that are made up of Carbon, and how CO2 is essential for plant life and thus animal life, and the demonization of both Carbon and CO2, is truly beyond my admittedly limited understanding…

But I do understand, they are not interested in the truth – they believe in, and want to believe in, fairy tales, not reality. Why people who believe in fairy tales have such sway, such weight, as to influence public policies, is another thing I cannot understand…

More renewable fantasy. Unfortunately many believe all this malarkey and think if we just go all in for renewables nothing will change for them and the world will be saved. The biggest misconception being grid level electrical storage capable of running cities and industry. Nothing but propaganda being fed to the masses.

The only serious alternative to fossil fuel based power plants are nuclear power plants that do not burn fossil fuels.

The reality is that, based on the paleoclimate record and the work done with models, the climate change we have been experiencing is caused by the sun and the oceans over which mankind has no control. Despite the hype, there is no real evidence that CO2 has any effect on climate and there is plenty of scientific rationale that the climate sensitivity of CO2 is zero. Hence stopping all CO2 emissions will have no effect on climate. But even if we could somehow stop the Earth’s climate from changing, extreme weather events and sea level rise would continue because they are both part of the current climate.

they should invest in large-scale energy storage projects as the most economical way to meet their carbon targets

1) The only such storage device available today is battery. The amount of batteries needed to cover several hours of household usage would cost in the 10’s of thousands of dollars and would last a few decades at most before it would have to be replaced.
2) Once again, the AGW warriors are relying on someone else to pick up the tab for their green dreams.

Will the so called fossil fuels go out of fashion ? Judging by the kind of “trucks” involved, one might conclude that Russia has very serious intentions to further prospect and develop oil & mining in the deep north (those who can, please translate):

1,450 tons of dirty coal to make the steel for the tower and the rebar for the pad. Many thousands of cubic feet natural gas to dehydrate gypsum and make concrete pad. The blades are resin/fiberglass. 18 semitrucks to deliver one tower assembly. Paint and primer for the tower.

“With more accurate information, consumers can move flexible consumption to times of the day when grid power is cleanest. “

These authors are true morons. They certainly don’t understand economics and what drives market decisions. It’s magical thinking that consumers are going to move consumption when grid is “cleanest” without a strong price incentive to overcome inconveniences. As such, they need to stick to their CCS engineering fantasies and stop thinking-writing about what consumers should do, because they clearly are clueless morons on human behavior and economic choices in a free market.

Consumers respond to prices/cost vs. convenience they can afford. That’s it. This is the same kind of idiotic thinking that Dave Middleton constantly fights back against with idiots claiming the oil and gas industry should reduce production to reduce emissions. Hello… they are in the business to make money selling a legal product. Similarly, if it’s 95F outside at 10pm and a parent needs to keep running my A/C so the kids can sleep, well the a/c is going to run.
Similarly, consumers aren’t going to care about their own CO2 footprint, anymore than Al Gore cares about his and his mansions and jet travel.

What these two morons semi-engineers don’t seem to grasp is the elites with their many millions or billions of personal net worth could give rat’s butt about the little guy. They have their private jets, their 3 homes, and vacations and maybe big boat. Higher electricty costs is a tiny part of their disposaable monthly income.

When will rentseeking morons like these two Stanford “geniuses” stop carrying water for the elitists and start being honest brokers of science and engineering?

How can one be in a prestigious university and be such a huge idiot like these two authors?

The Average price is noted as $.2441 kWh. This value underestimates the actual average as PG&E’s customers are not received a Climate Credit in their May bill. Hence customer will being paying an additional $27.70 on average in May.

I would like to see a calculation of the amount of electricity a wind turbine generator manufacturing plant needs to produce one wind turbine at a time, including blades, and correlate that to the number of same sized wind turbines needed to supply that power. Include calculation of number of wind turbines of that size needed to produce electricity needed to reduce calcium carbonate to lime for cement needed for concrete base. Include number of turbines needed to charge EV trucks delivering said cement and other construction materials.

Finally, calculate whether output of turbine plant could keep up with the failure rate of turbines in the 2 wind farms. I can imagine a wind farm powering turbine and cement production facilities with total output consumed by replacement needs of that very wind farm.

re: “I would like to see a calculation of the amount of electricity a wind turbine generator manufacturing plant needs to produce one wind turbine at a time, ”

As a starting point, what is the cost of said completed and installed wind turbine?

Then, what is the operational cost per year from date of install?

Also include cost of high voltage and medium voltage ‘plant’ necessary to bring all this electricity back to ‘load centers’ made up of people, buildings and residences. Some of the high cost of wind is on account of wind farms being located some distance away from ‘load centers’ (population centers) and therefore require HV transmission facilities to bring that energy back to the “big cities”.

“In Great Britain, for example, grid carbon intensity is currently lower at night, meaning different types of renewable investments or consumption behaviors might be better. ”

No, that is a false assumption. Yes carbon (O2) is lower at night as the proportion of the load following fossil fuel stations is lower. Move load to the night from the day as per ‘ consumption behaviors might be better’ will simply mean that the CO2 emission increase at night as fossil fuel generators increase output to match the load.
I don’t think the authors quite understand how power is generated for the grid?

Here in the UK we can see the current status of the National Grid on a site called Gridwatch, and I have been checking it daily for a while. We have a lot of offshore wind farms, and on a good day they can supply about 30% of demand. We have also replaced coal with gas. One day recently wind only managed 0.6% of demand, and gas was ramped up to 22% extra over normal that day. That’s why wind can never be carbon free.

And it’s here where the rubber meets the street. Those yearly averages are nothing but one method to shift costs renewables should be bearing over to the fossil generation assets. A truly honest company would only state their energy that actually came from renewable assets as their renewable share. Buying fossil power over nighttime and selling excess solar power during daytime at a guaranteed price (above market) just shots excess power into the grid when it’s not needed pushing power prices down for the others. We need a database of all those companies that signal virtue with this fraud and cut their possibility of getting fossil power during night or at least don’t guarantee fixed prices for their unneeded solar daypower. Right now, they make power more expensive for the average user which shifts the cost of renewable power en more towards those that can least afford it.

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